Plasmid virulence profiles of verotoxigenic Escherichia coli isolated in Argentina.

SANSO, A.M., FRANCI T., BUSTAMANTE A.V., PARMA A.E., LUCCHESI P.M.A.

Amsterdam

Simposio; 8th International Symposium on Shiga Toxin (Verocytotoxin) ? producing Escherichia coli infections (VTEC2012); 2012

Escherichia coli (VTEC) group is very diverse, being E. coli O157:H7 the most common serotype associated with sporadic cases and large outbreaks of hemolytic uremic syndrome in many countries. However, there is growing concern about the risk to human health associated with non-O157 VTEC serotypes. All clinical isolates of E. coli O157:H7 possess a large putative virulence plasmid called pO157 and similar plasmids are commonly found in non-O157 VTEC strains, presenting a considerable variability. Since there is little information about the plasmid genetic composition of native strains of VTEC, the raised aim was to characterize a selection of O157:H7 and non-O157:H7 VTEC strains in relation to some putative virulence factors located in the plasmids, to analyze the different combinations of these genes and to establish if some kind of relationship exists between these profiles and the serotypes.We have characterized a total of 208 VTEC isolates from Argentina belonging to 49 serotypes, collected from cattle, foods and humans, for the presence of plasmid-encoded genes: epeA (serine-protease), espP (extracellular serine protease), katP(periplasmic catalase-peroxidase), stcE(zinc metalloprotease) and subA (subtilase cytotoxin). The epeA gene was detected by a monoplex PCR and the remaining ones, by a pentavalent PCR assay that also detects . The isolates had been analyzed in relation to other plasmid-encoded genes, ehxA and saa, in previous studies.The most commonly detected gene was espP, which was present in 182 (87%) of the VTEC strains tested. The gen katP was found in 36 strains (17%) whereas epeA subA stcE were present in frequencies ranging from 7 to 12%. The ehxA gene, present in 47% of the isolates, was usually detected in combination with other plasmidic genes. Those strains that were positive for subA harbored neither stcE katP; was present only in O157:H7 strains, and katP never appeared simultaneously with saa. Taking into account the 7 encoded-plasmid genes, twelve virulence profiles were observed, being espP+ the most prevalent one (98 isolates), whereas katP espP+ ehxA+ (22 isolates) prevailed among VTEC isolates belonging to O26:H11, O38:H39, O118:H16, O145:NM, O146:NM, O165:NM and O177:NM serotypes. Some serotypes presented only one plasmid profile whereas others, such as O20:H19, showed up to 4 different profiles. The profile katP espP stcE ehxA+ was only present in O157:H7 isolates and in nine VTEC isolates it was not possible to detect any of the 7 plasmidic genes. In synthesis, our results show that VTEC strains can possess different combinations of plasmid-encoded virulence genes and even strains belonging to the same serotype can differ in relation to their plasmid genetic composition.